Voltage sense circuit

ABSTRACT

power supply module comprises a voltage converter coupled to first and second inputs. The voltage converter comprises a boosting circuit configured to boost an input voltage and comprises an input voltage selector (IVS) selectively connect and disconnect the first and second inputs to the boosting circuit. A first sensing circuit is coupled to the first input and comprises a pair of inputs coupled to the first input, a rectifier assembly, a resistor bank coupled between the pair of inputs and the rectifier assembly, a sense resistor coupled to the rectifier assembly, and a voltage sensor coupled to the sense resistor. A DC converter is configured to generate and supply an auxiliary voltage to the first sensing circuit. The resistor bank filters an electromagnetic interference (EMI) signal transmitted from the DC converter to a value below a threshold value.

FIELD

The present disclosure relates to the technical field of power suppliesand in particular to a voltage sense circuit.

BACKGROUND

A power supply typically converts an incoming voltage into a different,output voltage. For example, an alternating current (AC) input voltagemay be converted to a DC voltage for use by electronic equipment. Apower supply may use multiple inputs coupled to respective voltagesupplies for redundant operation. In a scenario where a primary sourceon a first input becomes undesirable, the power supply may switch to analternate source on a second input to continue to deliver output power.

When the input source is an AC source, consideration for minimizing oreliminating noise due to electromagnetic interference (EMI) may resultin the use of an EMI blocker such as a common-mode choke. Thecommon-mode choke, however, can be a relatively large device occupying alarge amount of space on a printed circuit board (PCB) and may not bedesirable upstream of a voltage sensing circuit in a power supply with ahigh input power density requirement.

OVERVIEW

In accordance with one aspect, a power supply module comprises a firstinput configured to receive a first input voltage, a second inputconfigured to receive a second input voltage, an output configured tosupply a power supply voltage, and a voltage converter coupled to thefirst and second inputs and to the output. The voltage convertercomprises a boosting circuit configured to boost one of the first inputvoltage and the second input voltage, an input voltage selector (IVS)coupled to the boosting circuit and coupled to the first and secondinputs to selectively connect and disconnect the first and second inputsto the boosting circuit, a first sensing circuit coupled to the firstinput, a control circuit coupled to the IVS and to the first sensingcircuit, and a direct current (DC) converter coupled to the boostingcircuit. The first sensing circuit comprises a pair of inputs coupled tothe first input, a rectifier assembly, a resistor bank coupled betweenthe pair of inputs and the rectifier assembly, a sense resistor coupledto the rectifier assembly, and a voltage sensor coupled to the senseresistor. The control circuit is configured to control the IVS to selectone of the first input and the second input based on a sense signalreceived from the first sensing circuit. The DC converter is configuredto generate an auxiliary voltage and to supply the auxiliary voltage tothe first sensing circuit. An electromagnetic interference (EMI) signaltransmitted from the DC converter to the first sensing circuit isfiltered to a value below a threshold value by the resistor bank.

In accordance with another aspect, a power supply unit comprises a powersupply voltage input configured to receive a source voltage from each ofa plurality of voltage sources, a power supply voltage output configuredto supply a power supply voltage, and one or more power supply modulescoupled to the power supply voltage input and to the power supplyvoltage output. Each power supply module comprises a pair of voltageinputs coupled to the power supply voltage input, an output coupled tothe power supply voltage output, and a voltage converter. The voltageconverter comprises an input voltage selector (IVS) coupled to the pairof voltage inputs and configured to transmit the source voltage from oneof the plurality of voltage sources, a boost circuit coupled to the IVSand configured to boost the source voltage from the one of the pluralityof voltage sources, a first sensing circuit, a control circuit coupledto the IVS and to the first sensing circuit, and a direct current (DC)converter coupled to the boost circuit. The first sensing circuitcomprises a sensor input coupled to a first input of the pair of voltageinputs, a rectifier assembly, a plurality of resistors coupled betweenthe sensor input and the rectifier assembly, a sense resistor coupled tothe rectifier assembly, and a voltage sensor coupled to the senseresistor. The control circuit is configured to control the IVS to selectone of the pair of voltage inputs based on a sense signal received fromthe first sensing circuit. The DC converter is configured to generate afirst auxiliary voltage and to supply the first auxiliary voltage to thefirst sensing circuit. An electromagnetic interference (EMI) signaltransmitted from the DC converter to the first sensing circuit isfiltered to a value below a threshold value by the plurality ofresistors.

In accordance with another aspect, a method of manufacturing a powersupply module comprises forming a first sensing circuit having a sensorinput and a sensor output and forming a voltage converter having atleast two inputs configured to receive respective input voltages.Forming the first sensing circuit comprises coupling a resistor bank tothe sensor input, coupling a rectifier assembly to the resistor bank,coupling a sense resistor to the rectifier assembly, and coupling avoltage sensor to the rectifier assembly. The resistor bank is seriallycoupled between the sensor input and the rectifier assembly. Forming thevoltage converter comprises coupling an input voltage selector (IVS) tothe at least two inputs, coupling a boosting circuit to the IVS,coupling a direct current (DC) converter to the boosting circuit,coupling the first sensing circuit to one of the at least two inputs andto the DC converter, and coupling a control circuit to the IVS and tothe first sensing circuit. The boosting circuit is configured to boostthe input voltage, and the DC converter configured to supply anauxiliary voltage. The control circuit is configured to receive a firstsense signal from the first sensing circuit and control the IVS toselectively transmit one of the respective input voltages to theboosting circuit based on the first sense signal. The first sensingcircuit is configured to receive the auxiliary voltage from the DCconverter and reduce an electromagnetic interference (EMI) signaltransmitted from the DC converter to a value below a threshold value viathe resistor bank.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout embodiments of the present disclosure.

In the drawings:

FIG. 1 is a block diagram of a power supply unit according to anembodiment of the present disclosure.

FIG. 2 is a block diagram of a voltage converter according to anembodiment of the present disclosure.

FIG. 3 is a schematic block diagram of a sensing circuit according to anembodiment of the present disclosure.

FIG. 4 is a schematic block diagram of a portion of a voltage sensoraccording to an embodiment of the present disclosure.

FIG. 5 illustrates an example schematic block diagram of a portion ofthe DC converter of FIG. 2 according to an embodiment of the presentdisclosure.

FIG. 6 is a schematic block diagram of a voltage converter according toanother embodiment of the present disclosure.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the present disclosure to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present disclosure. Note that correspondingreference numerals indicate corresponding parts throughout the severalviews of the drawings.

DETAILED DESCRIPTION

Examples of the present disclosure will now be described more fully withreference to the accompanying drawings. The following description ismerely exemplary in nature and is not intended to limit the presentdisclosure, application, or uses.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention which may be embodied inother specific structures. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention, which is defined by the claims.

FIG. 1 illustrates a block diagram of a power supply unit 100 accordingto an embodiment of the present disclosure. Power supply unit 100includes one or more power supply modules 102, 104, 106 configured toconvert an input power into an output power. As illustrated, powersupply unit 100 includes three power supply modules 102, 104, 106;however, embodiments of the present disclosure may include more or lessthan three modules.

Each power supply module includes a pair of source inputs 108, 110 forrespectively receiving power from a first power source 112 and from asecond power source 114. In one embodiment, the first and second powersources 112, 114 are alternating current (AC) sources supplying powerfrom one or more AC sources such as the utility grid, generators, andthe like. Alternatively, one or both of the first and second powersources 112, 114 may be a direct current (DC) source supplying powerfrom one or more DC sources such as batteries, capacitor banks, and thelike. In an example, the first power source 112 is a three-phase ACsource from which a default AC feed is provided to the power supplymodules 102, 104, 106 in separate phases such that each power supplymodule receives a different phase from the power source 112. In thissame example, the second power source 114 may be another, distinctthree-phase AC source from which a backup AC feed is provided to thepower supply modules 102, 104, 106 in separate phases.

Each power supply module also includes a voltage converter 116configured to convert the voltage from one of the first and second powersources 112, 114 into a different form and deliver the converted voltageto an output 118. For example, voltage converters 116 may be configuredto convert the single-phase AC voltage received from the respectivesource input 108, 110 into a DC output voltage that is supplied from theoutput 118 to a voltage bus 120. From the voltage bus 120, the DC outputvoltage may be supplied to an output 122 of the power supply unit 100.

FIG. 2 illustrates a block diagram of a voltage converter 200 accordingto an embodiment of the present disclosure. The voltage converter 200may describe any one of the voltage converters 116 shown in FIG. 1 . Theinput voltages from the first and second power sources 112, 114 areprovided to an input voltage selector (IVS) 202, which includes a relay(not shown) for selecting the voltage/power to be converted. Forexample, as shown, IVS 202 couples the voltage/power from the firstpower source 112 to be converted by the voltage converter 200. Anelectromagnetic interference (EMI) blocker 204 may be coupled to anoutput of the IVS 202 to block EMI transmitted through the IVS 202 frompropagating through to the voltage conversion blocks downstream.

A boosting circuit such as a power factor correction (PFC) circuit 206is configured to rectify and boost the input voltage from the IVS 202.The PFC circuit 206 may, therefore, rectify an AC voltage from the IVS202 and boost the rectified voltage to supply a DC high voltage 208. ThePFC circuit 206 may accept a voltage waveform in any shape, includingpure DC voltage, and output the DC high voltage 208. A high-capacitycapacitor 210 coupled to the output of the PFC circuit 206 may be usedto maintain the DC high voltage 208 for a short holding time should theDC high voltage 208 be briefly lost from the PFC circuit 206.

A DC/DC converter 212 is coupled to receive the DC high voltage 208 fromthe PFC circuit 206 and convert the DC high voltage 208 to a DC lowvoltage output 214 such as 12 Vdc, 5 Vdc, and the like. The DC/DCconverter 212 includes a transformer that provides isolation and formspart of the voltage conversion function. A main control circuit 216 iscoupled to the IVS 202, the PFC circuit 206, and the DC/DC converter 212and provides control signals for their operation. The control circuit216 is configured to receive signals from a pair of sensing circuits218, 220, each coupled to a respective input power source 112, 114. Thesensing circuits 218, 220 operate to sense the input voltages Vin 1 222and Vin 2 224 from input power sources 112, 114 and supply sense signals226, 228 to the control circuit 216, which decides whether the inputvoltages 222, 224 meet operating requirements and thresholds. Based onthe decision, the control circuit 216 decides which input power source112, 114 to use and controls the IVS 202 accordingly. For example, ifboth input power source 112, 114 are operating within parameters, thefirst power source 112 may be always selected based on its designationas the default source as long as its parameters meet the incomingvoltage thresholds. If, however, the voltage 222 from the first powersource 112 becomes out-of-spec or otherwise falls outside operationalthresholds and/or limits, the control circuit 216 may control the IVS202 to use the backup input voltage 224 from the second power source 114if the sense signal 228 from the second input sensing circuit 220indicates that its power is within operational parameters. After thevoltage input 222 from the first power source 112 returns to meet theappropriate operational parameters, its voltage may be once againselected as the voltage to be used through control of the IVS 202 by thecontrol circuit 216.

FIG. 3 illustrates a schematic block diagram of the sensing circuits218, 220 according to an embodiment. A pair of voltage inputs 230, 232are directly coupled to inputs for the first or second power source 112,114 and receives Vin 1 222 or Vin 2 224 depending on which power source112, 114 the sensing circuit is coupled to. The voltage input 230 mayreceive a line voltage, for example, while the voltage input 232 mayreceive a neutral line voltage in an embodiment where the incomingvoltage is AC. A resistor bank 234 is coupled to the voltage inputs 230,232 and has one or more resistors coupled to each voltage input 230,232. As shown, for example, resistor bank 234 has two resistors 236, 238coupled to the voltage input 230 and two resistors 240, 242 coupled tothe voltage input 232. The resistors 236-242 can be large valueresistors (e.g., 330K ohms) and may be capable of handling largevoltages (e.g., 400 V) so that when combined, a high differential modevoltage surge (e.g., 1600 V) may be sustained without negative effects.For higher differential mode voltage surge requirements (e.g., 2000 V),for example, additional resistors may be coupled in series.

The input voltage 222, 224 passes from the resistor bank 234 to arectifier 244 that rectifies the input voltage 222, 224 (e.g., from ACto DC) and supplies the rectified voltage to a sense resistor 246, whichgenerates a sense voltage, V_(sense), supplied to a voltage sensor 248.In one example, rectifier 244 includes four diodes 250 arranged in afull-wave bridge rectifier arrangement. Referring to FIG. 4 , aschematic block diagram of a portion of the voltage sensor 248 of FIG. 3is shown. The voltage sensor 248 includes a comparator 252 having afirst input 254 for the sense voltage, V_(sense), and having a secondinput 256 for a reference voltage, V_(ref). The reference voltage,V_(ref), is designed so that a comparison of the sense voltage with thereference voltage controls a switch circuit 258 to indicate a status ofthe input voltage 222, 224. The switch circuit 258 may be switched on orswitched into a conductive state, for example, to indicate that theinput voltage 222, 224 meets the parameters for the incoming voltagethresholds. When the switch circuit 258 is switched off or in anon-conductive state, the input voltage 222, 224 may be indicated tofail one or more of the parameters set for allowable input voltages 222,224. The voltage sensor 248 illustrated in FIG. 4 , however, is merelyone example of a sensing circuit, and other embodiments may be usedwithout deviating from the scope of this disclosure. Referring to FIGS.3 and 4 , the output of the switch circuit 258 may be provided to anisolator 260 such as an optoisolator for generating the respective sensesignal 226, 228 sent to the control circuit 216 for deciding which powersource 112, 114 to use.

The resistor bank 234 obviates the placement of an inductive EMI chokeat the input of the sensing circuit 218, 220 for handling of EMI effectscoming from the power sources 112, 114. Instead, the resistor bank 234effectively filters any EMI noise to values below a threshold value. Theuse of the resistors 236-242 allows for the realization of space savingsin printed circuit board (PCB) real estate and cost compared with aninductive EMI choke (e.g., a toroid wound inductor) of equivalent EMIfiltering capacity.

Referring back to FIG. 2 , the voltage converter 200 also includes a DCconverter 262 to convert a portion of the DC high voltage 208 into oneor more auxiliary voltages 264, 266, 268, 270 for use throughout thevoltage converter 200. Referring to FIG. 5 , is illustrated, a pair ofvoltage inputs 272, 274 are coupled to the PFC circuit 206 to receive aportion of the DC high voltage 208 therefrom. A transformer 276 has aprimary winding 278 coupled to a switch 280 such as a transistor that iscontrolled by a switch control 282 to generate inductive voltages insecondary windings 284, 286, 288, 290 to produce the auxiliary voltages264, 266, 268, 270. While the illustrated example shows four auxiliaryvoltages, embodiments of the present disclosure contemplate that more orfewer auxiliary voltages may be supplied by the DC converter 262.

Referring back to FIG. 2 , first and second auxiliary voltages 264, 266may be provided to sensing circuits 218, 220 (as illustrated in FIG. 3), respectively. A third auxiliary voltage 268 may be provided to thePFC circuit 206 and to the control circuit 216. A fourth auxiliaryvoltage 270 may be provided to the DC/DC converter 212. Any EMI 292, 294experienced by or generated in the DC converter 262 may be transferredto the respective sensing circuits 218, 220 along with the auxiliaryvoltages 264, 266. With inadequate attenuation, the sensing circuits218, 220 may transfer the EMI through the rectifier 244 and voltageinputs 230, 232 back out to the power sources 112, 114, which isundesirable. However, the sensing circuits 218, 220 disclosed hereineffectively filter the EMI from the DC converter 262 via the resistorbank 234 to value levels below a threshold value prior to the EMIreaching the power sources 112, 114 according to embodiments of thepresent disclosure. Accordingly, larger and more costly EMIblocking/filtering components such as toroidally-wound inductive coilscan be avoided in the sensing circuitry such that no inductive coil forblocking EMI is placed between the rectifier 244 of the sensing circuits218, 220 and the source inputs 108, 110. The threshold value may bedecided by one or more regulatory rules defining the amount ofacceptable EMI in the industry. For example, EMI values above thethreshold value are typically labelled as failing EMI blockinginitiatives.

FIG. 6 illustrates a block diagram of a voltage converter 600 accordingto another embodiment of the present disclosure. The voltage converter600 has similar components depicted for the sensing circuit shown inFIG. 3 but the rectifier 244 is illustrated as a half-wave rectifier. Anappropriate selection of the reference voltage, V_(ref), may be used toindicate behavior of the input voltage 222, 224 based on using ahalf-wave rectified signal versus the full-wave rectified signalillustrated in FIG. 3 .

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of thepresent disclosure. Additionally, while various embodiments of thepresent disclosure have been described, it is to be understood thataspects of the present disclosure may include only some of the describedembodiments. Accordingly, the invention is not to be seen as limited bythe foregoing description but is only limited by the scope of theappended claims.

What is claimed is:
 1. A power supply module comprising: an inputvoltage selector (IVS) configured to selectively connect and disconnecta first input and a second input to a boosting circuit; a first sensingcircuit coupled to the first input and comprising a resistor bank; acontrol circuit coupled to the IVS and to the first sensing circuit, thecontrol circuit configured to control the IVS to select one of the firstinput and the second input based on a sense signal received from thefirst sensing circuit; and a direct current (DC) converter coupled tothe first sensing circuit and configured to generate an auxiliaryvoltage and to supply the auxiliary voltage to the first sensingcircuit; wherein an electromagnetic interference (EMI) signaltransmitted from the DC converter to the first sensing circuit isfiltered to a value below a threshold value by the resistor bank.
 2. Thepower supply module of claim 1, wherein the first sensing circuitfurther comprises: a pair of inputs coupled to the first input; arectifier assembly; a sense resistor coupled to the rectifier assembly;and a voltage sensor coupled to the sense resistor; wherein the resistorbank is coupled between the pair of inputs and the rectifier assembly.3. The power supply module of claim 2, wherein the resistor bankcomprises: one or more resistors coupled between the rectifier assemblyand a first input of the pair of inputs; and one or more resistorscoupled between the rectifier assembly and a second input of the pair ofinputs.
 4. The power supply module of claim 2, wherein the rectifierassembly comprises four diodes arranged in a full-wave bridge rectifierarrangement.
 5. The power supply module of claim 2, wherein the powersupply module is absent a toroidally-wound inductive coil between therectifier assembly and the first input for reducing EMI.
 6. The powersupply module of claim 2 further comprising a second sensing circuitcoupled to the second input and comprising: a pair of inputs coupled tothe second input; a rectifier assembly; a resistor bank coupled betweenthe pair of inputs of the second sensing circuit and the rectifierassembly of the second sensing circuit; a sense resistor coupled to therectifier assembly of the second sensing circuit; and a voltage sensorcoupled to the sense resistor of the second sensing circuit.
 7. Thepower supply module of claim 2, wherein the first sensing circuitfurther comprises an isolator coupled to the voltage sensor and to thecontrol circuit, the isolator configured to electrically isolate thefirst sensing circuit from the control circuit.
 8. The power supplymodule of claim 2, wherein the boosting circuit comprises a power factorcorrection circuit configured to convert a first input voltage from analternating current (AC) voltage into a DC voltage.
 9. The power supplymodule of claim 8, further comprising a DC/DC converter configured toconvert the DC voltage into a lower, output DC voltage.
 10. A powersupply unit comprising: a voltage converter comprising: an input voltageselector (IVS) configured to transmit a source voltage from one of aplurality of voltage sources; a first sensing circuit comprising: asensor input coupled to a first input of the IVS; and a plurality ofresistors coupled to the sensor input; a control circuit coupled to theIVS and to the first sensing circuit, the control circuit configured tocontrol the IVS to select the source voltage from a pair of voltageinputs based on a sense signal received from the first sensing circuit;and a direct current (DC) converter coupled to the first sensing circuitand configured to generate a first auxiliary voltage and to supply thefirst auxiliary voltage to the first sensing circuit; wherein anelectromagnetic interference (EMI) signal transmitted from the DCconverter to the first sensing circuit is filtered to a value below athreshold value by the plurality of resistors.
 11. The power supply unitof claim 10, wherein the power supply unit further comprises: a powersupply voltage input configured to receive a source voltage from each ofthe plurality of voltage sources; a power supply voltage outputconfigured to supply a power supply output voltage; a power supplymodule coupled to the power supply voltage input and to the power supplyvoltage output, the power supply module comprising: a pair of voltageinputs coupled to the power supply voltage input; an output coupled tothe power supply voltage output; and the voltage converter.
 12. Thepower supply unit of claim 11, wherein the sensor input comprises afirst sensor input coupled to a first input connection of a first inputof the pair of voltage inputs; wherein the sensor input furthercomprises a second sensor input coupled to a second input connection ofthe first input of the pair of voltage inputs; wherein the first sensingcircuit further comprises a rectifier assembly; and wherein theplurality of resistors comprises: one or more resistors coupled betweenthe rectifier assembly and the first sensor input; and one or moreresistors coupled between the rectifier assembly and the second sensorinput.
 13. The power supply unit of claim 12, wherein the first inputconnection comprises a line voltage of the first input of the pair ofvoltage inputs; and wherein the second input connection comprises aneutral line voltage of the first input of the pair of voltage inputs.14. The power supply unit of claim 12, wherein the power supply moduleis absent a toroidally-wound inductive coil between the rectifierassembly and the first input of the pair of voltage inputs for reducingEMI.
 15. The power supply unit of claim 11 further comprising a secondsensing circuit comprising: a sensor input coupled to a second input ofthe pair of voltage inputs; a rectifier assembly; a plurality ofresistors coupled between the sensor input of the second sensing circuitand the rectifier assembly of the second sensing circuit; a senseresistor coupled to the rectifier assembly of the second sensingcircuit; and a voltage sensor coupled to the sense resistor of thesecond sensing circuit.
 16. The power supply unit of claim 11, whereinthe power supply module comprises a first power supply module configuredto receive a first phase of the source voltage from a first voltagesource of the plurality of voltage sources and to receive a first phaseof the source voltage from a second voltage source of the plurality ofvoltage sources; wherein the power supply unit further comprises asecond power supply module configured to receive a second phase of thesource voltage from the first voltage source of the plurality of voltagesources and to receive a second phase of the source voltage from thesecond voltage source of the plurality of voltage sources; and whereinthe power supply unit further comprises a third power supply moduleconfigured to receive a third phase of the source voltage from the firstvoltage source of the plurality of voltage sources and to receive athird phase of the source voltage from the second voltage source of theplurality of voltage sources.
 17. The power supply unit of claim 10,wherein the first sensing circuit further comprises an optoisolatorcoupled to the control circuit, the optoisolator configured to transmitthe sense signal to the control circuit.
 18. The power supply unit ofclaim 10, wherein the voltage converter comprises a power factorcorrection circuit configured to convert the source voltage from the oneof the plurality of voltage sources from an alternating current (AC)voltage into a DC voltage; and wherein the voltage converter furthercomprises a DC/DC converter configured to convert the DC voltage into alower, output DC power supply voltage.
 19. A method comprising:transmitting, via an input voltage selector (IVS), a source voltage fromone of a plurality of voltage sources to a power supply module;generating, via a sensing circuit, a sense voltage based on the sourcevoltage, wherein the sensing circuit comprises a sensor input, a senseresistor, and a resistor bank coupled between the sensor input and thesense resistor; comparing the sense voltage to a reference voltage;transmitting a sense signal to a control circuit; controlling the IVS toselect the source voltage based on the sense signal; and generating andsupplying an auxiliary voltage to the sensing circuit; and filtering anelectromagnetic interference (EMI) signal within the auxiliary voltageto a value below a threshold value via the resistor bank.
 20. The methodof claim 19, wherein filtering the EMI signal comprises filtering theEMI signal without a toroidally-wound inductive coil.